The present invention is directed to a strain relief system for use with a detector card which carries a plurality of detector cans to which are attached optical fibers. More particularly, the present invention relates to a strain relief system for securing each optical fiber pigtailed into a detector can mounted on a PC board such that the optical fibers are prevented from breaking, are maintained in their proper position and such that proper cooling is allowed of the protector cans.
In fiber optic detection systems, it is typical to utilize a plurality of detector cans which are mounted on a PC board or similar mounting material. An optical fiber is pigtailed into each detector can and is precisely positioned over a photodiode. Movement of the detector card, for example, while handling the card during its installation, can result in the pulling away of the optical fibers from the detector cans. That results in the misalignment of the pulled-away fiber with its photodiode, causing a degradation of the measurement capability of the fiber optic detection system. Worse, it is possible that the movement of the detector card could result in the pulling out of one or more optical fibers from their respective cans, or the breaking or bending of the optical fibers. Obviously, such conditions would severely degrade the operation of the fiber optic detection system using such a damaged detector card.
There is presently no known strain relief system which is designed to work with multi-can detector cards that utilize pigtailed optical fibers. While a similar detector card has been used by Lockheed Aircraft Services Company, no strain relief was designed or utilized. As a result, many of the optical fibers utilized with the Lockheed detector cards snapped or pulled away from their detector cans during handling of the cards. Also, although strain relief fittings are available from Heyco Molded Products Company, Inc. of Kenilworth, N.J. and monocoils were known for the protection of fiber optic cables, they have not previously been used in connection with a detector card strain relief system for providing protection as well as strain relief for a detector card such as that described above used in a fiber optic detection system.
The present invention is therefore directed primarily to the protection of the optical fibers which are pigtailed into respective detector cans on a detector card such that they are precisely positioned over a photodiode. The present invention eliminates the danger of the optical fibers pulling away from or out of the detector can during handling by keeping the optical fibers stationary with respect to the detector cans. Thus, using the present invention, a detector card can be moved without having to worry about moving the optical fibers along with it. The inventive assembly moves both of them at the same time. In addition, the protective monocoil, which is a flexible wire wrap covered with vinyl, keeps the fibers from getting crushed or snapped in half during movement of the card, or otherwise.
The present invention also allows for the cooling of the detector cans during operation of the fiber optic detector system of which the detector card forms a part. This is an important feature since the difference in temperature between all of the cans must be within one degree Celsius in order to maintain uniform performance. Since the instant detector card strain relief assembly is designed to keep the optical fibers in line with their respective detector cans, air is allowed to smoothly pass between the fibers and effectively cool the plurality of detector cans.
The detector card strain relief system of the present invention is also designed to keep the optical fibers straight as they enter their respective detector cans. That not only reduces strain, but keeps light from breaking out of the optical fibers. If an optical fiber is bent too much, the fiber will not be able to support the additional modes that will develop. Thus, the energy in those modes will leak out of the optical fiber with the result that a reduced amount of light will enter the detector and an erroneous signal will be measured. The optical fibers are more suspectable to such leakage at the detector cans since the fibers are rigidly attached to the cans and a kink can develop there more easily.